Self-unloading magnetic coupler

Abstract

In a magnetic coupler, a pair of magnet rotors is slidably mounted on rods. Ferrous material on the conductor rotors attracts the permanent magnets in the magnet rotors. Under static or relative static conditions, the attractive force urges the magnet rotors toward the conductor rotors to create a minimum, operational air gap therebetween. When there is a significant relative rotational velocity between the magnet rotors and the conductor rotors, a repulsion force urges the rotors apart. During start-up, latch arms retain the magnet rotors apart from the conductor rotors by a larger, soft-start air gap. During operation, centrifugal force moves the latch arms out of their active position. If the rotational speed of the load shaft decreases rapidly during operation, the magnet rotors move apart from the conductor rotors by a still larger, fully disengaged air gap.

What is claimed is:  
     
       1. A coupler, comprising: 
       first and second rotary hubs, each having a rotary axis;  
       two coaxial magnet rotors each containing a respective set of permanent magnets;  
       two coaxial conductor rotors each having a non-ferrous electroconductive ring spaced by a gap from a respective one of the sets of magnets;  
       a first two of the rotors being spaced apart a fixed axial distance and being mounted as a unit on the first hub to rotate in unison therewith;  
       two end plates connected by rods and being mounted to rotate in unison with the second hub, the remaining two of the rotors being moveable axially on the rods with respect to the first two of the rotors, the rotors being configured to move into three distinct configurations, a first position with a minimum air gap, an intermediate position with an intermediate air gap greater than the minimum air gap, and a second position with a maximum air gap greater than the intermediate air gap; and  
       magnet attracting material associated with the conductor rotors, the magnet attracting material being sized and shaped to interact with respective of the sets of permanent magnets and to magnetically bias the rotors into the first position, wherein overloading of the coupler caused by sufficient slip between the magnet and conductor rotors results in an axial thrust opposing and exceeding the bias to move the magnet and conductor rotors out of the first position.  
     
     
       2. The coupler of  claim 1 , further comprising adjustable stops positioned between the end plates and the remaining two of the rotors for adjusting the gap. 
     
     
       3. A coupler according to  claim 1  in which both of the rotors in the unit are conductor rotors; and 
       the remaining rotors are magnet rotors located between the conductor rotors.  
     
     
       4. A coupler according to  claim 1  in which the stops comprise set screws passing through the end plates and arranged to contact the remaining two of the rotors. 
     
     
       5. A coupler, comprising: 
       first and second rotary shafts, each having a rotary axis;  
       two coaxial magnet rotors each containing a respective set of permanent magnets;  
       two coaxial conductor rotors each having a non-ferrous electroconductive ring spaced by a gap from a respective one of the sets of magnets;  
       a first two of the rotors being spaced apart a fixed axial distance and being mounted as a unit on the first shaft to rotate in unison therewith;  
       the remaining two of the rotors being mounted to rotate in unison with the second shaft and to be moveable axially in opposite directions with respect to the second shaft into and out of a magnetically coupled relationship with the first two of the rotors;  
       magnet attracting material associated with the conductor rotors such as to interact with respective of the sets of permanent magnets and magnetically bias the rotors into the coupled relationship, wherein relative rotation between the magnet and conductor rotors in the form of slip results in an axial force counter to the bias urging the rotors out of the coupled relationship; and  
       latch elements carried by the remaining rotors and arranged when in an active position to limit axial movement of the remaining rotors due to repelling forces during startup of the coupler, the latch elements being moveable responsive to centrifugal force to an inactive position whereby the coupler is able to fully disengage due to repelling forces following startup.  
     
     
       6. A coupler according to  claim 5  in which there is a stop associated with the rotors limiting the minimum size of the gap. 
     
     
       7. A coupler according to  claim 6  in which the minimum air gap is adjustable by adjustment of the stop so as to be such that after startup a slip between the shafts from an overload condition causes axial thrust exceeding the bias, thereby disengaging the coupler. 
     
     
       8. A coupler according to  claim 5  in which each of the latch elements is arranged to swing on a swing axis from an active position parallel to the rotary axis to an inactive position directed radially outward from the rotary axis. 
     
     
       9. A coupler according to  claim 8  in which each latch element has a spring arranged to yieldingly resist swinging thereof away from its active position at low rotational speeds. 
     
     
       10. A magnetic coupler for preventing pop-off during startup and allowing pop-off after startup, comprising: 
       first and second rotary shafts, each having a rotary axis;  
       two coaxial magnet rotors, each having a set of permanent magnets;  
       two coaxial conductor rotors positioned adjacent the respective magnet rotors, each conductor rotor having a non-ferrous, electroconductive ring spaced by a first gap from the respective magnet rotor;  
       a first two of the rotors being spaced apart from each other by a fixed axial distance and being mounted as a unit on the first shaft to rotate in unison therewith;  
       the remaining two of the rotors being mounted to rotate in unison with the second shaft and to be moveable axially with respect to the second shaft in relationship with the first two of the rotors;  
       magnet attracting material coupled to each of the conductor rotors to magnetically bias the magnet rotors toward the conductor rotors, the magnet attracting material being sized, shaped and positioned such that a repulsive force caused by significant relative rotation between the magnet rotors and the conductor rotors is sufficient to counter the bias and urge the remaining two rotors apart from the first two rotors; and  
       at least one latch element carried by the second shaft, the at least one latch element being movable under centrifugal force between an active position in which the at least one latch element limits movement of the remaining two of the rotors to a first distance apart from the first two rotors, and an inactive position in which the at least one latch element limits movement of the remaining two of the rotors to a second distance apart from the first two rotors, the second distance being greater than the first distance.  
     
     
       11. The magnetic coupler of  claim 10  wherein the first distance is predetermined to provide the coupler with soft-start characteristics. 
     
     
       12. The magnetic coupler of  claim 10  wherein the second distance is predetermined to provide the coupler with indefinite running characteristics. 
     
     
       13. The magnetic coupler of  claim 10  wherein the magnet attracting material is in the form of a ferrous material distributed about the perimeter of the conductor rotors. 
     
     
       14. The magnetic coupler of  claim 10  wherein the magnet attracting material is in the form of a ring of ferrous material concentrically positioned about the conductor rotors. 
     
     
       15. The magnetic coupler of  claim 10  wherein the magnet attracting material is in the form of a ring of ferrous material concentrically positioned about the conductor rotors, and is located on a face of the conductor rotors opposite the respective magnet rotors. 
     
     
       16. The magnetic coupler of  claim 10  wherein the at least one latch element comprises a latch arm pivotal between the active and inactive positions. 
     
     
       17. The magnetic coupler of  claim 10  wherein the at least one latch element comprises a fixed arm projecting inwardly from one of the remaining two rotors and a shutter on the other of the remaining two rotors, the shutter being aligned with the fixed arm and being movable between the active position wherein the shutter obstructs passage of the fixed arm, and the inactive position wherein the shutter allows the fixed arm to at least partially enter an opening in the other of the remaining two rotors. 
     
     
       18. The magnet coupler of  claim 10  wherein the at least one latch element is adjustable to change the first distance. 
     
     
       19. A magnetic coupler for preventing full disengagement during startup and allowing full disengagement after startup, comprising: 
       first and second rotary shafts, each having a rotary axis;  
       a magnet rotor having a set of permanent magnets;  
       a conductor rotor positioned adjacent the magnet rotors, the conductor rotor having a non-ferrous, electroconductive ring spaced by a first gap from the magnet rotor;  
       a first of the rotors being mounted on the first shaft to rotate in unison therewith, the first of the rotors being axially fixed with respect to the first shaft;  
       the remaining of the rotors being mounted to rotate in unison with the second shaft and to be moveable axially with respect to the second shaft into and out of a magnetically coupled relationship with the first of the rotors;  
       magnet attracting material coupled to the conductor rotor to magnetically bias the magnet rotor toward the conductor rotor and to urge the rotors into a coupled relationship, the magnet attracting material being sized, shaped and positioned such a repulsive force caused by significant relative rotation between the magnet rotor and the conductor rotor is sufficient to counter the bias and urge the rotors out of the coupled relationship; and  
       at least one latch element movable by centrifugal force between an active position in which the at least one latch element limits movement of the remaining of the rotors to a first distance out of the coupled relationship, and an inactive position in which the at least one latch element limits movement of the remaining of the rotors to a second distance out of the coupled relationship, the second distance being greater than the first distance.